1. Field of the Invention
The present invention relates to a coating paper formed by providing a coating layer on a substrate paper which easily swells, disperses or dissolves by contact with water and a method for the preparation thereof, and an adhesive sheet formed by providing an adhesive layer on a non-coating surface of said coating paper. More in detail, the present invention is a coating paper prepared by providing a coating layer having a characteristic for various printing methods such as offset printing, gravure printing, thermal recording method, ink-jet recording method or laser beam printing method on a substrate paper characterized in that at least a part may swell, disperse or dissolve by water, which can be preferably used for a use such as a label for a returnable container utilizing a special feature that a coating layer is easily removed by removing a part of the paper or by a dispersion or through dissolving, and further relates to a method for the preparation of said coating paper.
2. Description of the Prior Art
Recently, environmental problems are becoming an object of public interest, and a returnable container has broadly been given attention. Generally, to a returnable container, an adhesive label has been applied having an adhesive layer at a rear surface of a coating paper, on the surface of which letters or patterns are printed. However, after used, said label should be removed (released) from the container, but complicated washing work is necessary. For the purpose of making said removing work easy, investigations to improve the removing (releasing) ability of a label by using a water-soluble adhesive to an adhesive layer are carried out. However, in this case, since a coating layer and a substrate paper prevent water from entering into an adhesive layer, the remarkable effect cannot be accomplished.
To solve said problem, a water-decaying adhesive sheet characterized by providing a coating layer suited for various recording systems on a substrate paper prepared by using a water-soluble material or water-dispersible material and providing an adhesive layer on a non-coating layer is disclosed in Patent Document 1.
The construction of a water-decaying thermally sensitive recording sheet disclosed in Patent Document 1 and a water-decaying adhesive sheet which uses said water-decaying thermally sensitive recording sheet is characterized by providing a specific filling layer and a coating layer (thermally sensitive recording layer) on a water-soluble or water-dispersible substrate paper and providing an adhesive layer on a non-coating layer, and make it possible to remove a label easily from a returnable container by using a water-soluble paper or water-dispersible paper as a substrate paper. In the present invention, a water-soluble paper is a paper which has a feature of dispersing fibrously in water within a very small amount of time of 5-20 seconds and partially dissolves in water, and a method for the preparation thereof is disclosed in Patent Documents 2 and 3. That is, various additives (filler, sizing agent, dye or pigment) are added to water-soluble fibers, if necessary, and can be prepared by ordinary paper making methods. Said water-soluble paper is not only actually used as a printing paper or a writing paper but also can be used as a water-soluble adhesive label or a water-soluble bag by providing adherence or heat-sealing ability by carrying out secondary processing such as coating, adhering or laminating. Further, in the present invention, a water-dispersible paper is a paper which has a characteristic of disaggregating in water and becoming small fragments, and is mainly used as a toilet tissue which can be disposed in a flush toilet after being used.
Further, in general, in a case when a coating liquid consisting of an aqueous solution of a water-soluble resin or water dispersion of a water-insoluble resin is coated on a substrate paper made of a water-soluble paper or water-dispersible paper using a bar coater method, knife coating method, roll coating method, blade coating method, die coating method or gravure coating method, then dried, a water-soluble paper or water-dispersible paper, which is a substrate paper, has a tendency to swell excessively and cause a problem of breaking in a coating machine.
To solve said problem, in Patent Document 1, the following methods are disclosed. That is, (1) forming a filling layer by coating and drying a water-soluble resin or a water-dispersible resin dissolved in an organic solvent by a publicly known method such as a bar coater method utilizing features that a water-soluble paper or water-dispersible paper do not disperse or dissolve in an organic solvent. (2) Forming a water-soluble filling layer using a water-soluble resin which can be applied by an extrusion method using an extrusion molding machine, and further forming a filling layer composed of a water-insoluble resin on the water-soluble filling layer.
However, a water-decaying thermally sensitive recording sheet and a water-decaying adhesive sheet using said water-decaying thermally sensitive recording sheet disclosed in Patent Document 1 has a problem that the manufacturing cost becomes high because an expensive organic solvent is used and an additional coating process besides a coating process of a coating layer (thermally sensitive recording layer) is necessary. Further, a decaying feature of a filling layer formed by coating an organic solvent coating using a water-soluble resin or water-dispersible resin which can dissolve in an organic solvent is inferior when compared with that of a water-soluble paper or water-dispersible paper used as a substrate material or with that of a coating layer provided on a substrate paper and, therefore, when washed by water, it is removed in a film state and causes a problem of stuffing a drainpipe.
Further, in Patent Document 4, a water-dispersible sheet formed by providing a coating layer on a substrate paper of a water-soluble paper or water-dispersible paper is disclosed. However, said sheet is not sufficient in its decaying feature by water in the suited grammage region as a substrate paper of coating paper.
As mentioned above, a coating paper which has both a good decaying feature by water and characteristic as a coating paper (printing aptitude) and a method for the preparation thereof have not been accomplished yet.
Patent Document 1: JP2004-314623A Publication
Patent Document 2: Japanese Patent S43-1214 Publication
Patent Document 3: Japanese Patent S48-27605 Publication
Patent Document 4: JPH09-49188A Publication